In-use stability testing, an essential requirement in drug evaluation
In-use stability testing is a fundamental process within the development and quality control of medicinal products. Its purpose is to ensure that a pharmaceutical product maintains its physicochemical and microbiological properties after the container has been opened and throughout its period of use.
Unlike long-term or accelerated stability studies, in-use stability testing focuses on the actual behavior of the medicine once it begins to be used, making it an essential tool to guarantee patient safety and treatment efficacy.
Importance of in-use stability testing
Multidose products such as eye drops, oral suspensions, injectable solutions, or topical preparations require special attention. Each opening of the container represents a potential entry of air, humidity, or microorganisms that may alter the composition of the drug.
In-use stability studies make it possible to evaluate whether the product maintains its quality under these exposure conditions. The results obtained serve to define the period of use after opening—information that the manufacturer must include in the labeling and package leaflet.
In this way, the risk of administering a degraded or contaminated medicine is avoided, as well as the unnecessary disposal of products that remain suitable for use.
Study design and methodology
The design of an in-use stability study depends on the nature of the drug and its route of administration. Typically, representative batches are used, subjected to simulated openings and controlled storage conditions.
During the study period, various parameters are evaluated at defined intervals, such as:
- Concentration of the active ingredient
- pH, color, viscosity, and physical appearance
- Level and effectiveness of the preservative
- Microbial load
- Compatibility of the contents with the container material
These tests must be carried out in accordance with Good Laboratory Practice (GLP) and the guidelines established by the European Medicines Agency (EMA) and the International Council for Harmonisation (ICH). Strict adherence to these standards ensures reliable and reproducible results.
Manufacturer responsibility and regulatory compliance
European legislation requires that every manufacturer demonstrate, through experimental studies, the in-use stability of the medicinal product. The results obtained support the information on storage conditions and duration after opening, which must be clearly stated on the product label.
In-use stability testing is therefore not merely a regulatory formality, but a scientific tool that ensures the quality, safety, and efficacy of a medicine throughout its entire period of use.
